1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and a method for detection of atrial fibrillation within a mean heart signal of a body.
2. Description of the Related Art
Generally, implantable cardiac monitors are implantable medical devices that monitor the electrical activity of the heart by using electrodes in contact with the body tissue. These electrodes are usually located at the case of the implanted medical device that is implanted under the skin of the chest close in vicinity of the heart. Alternatively the electrodes are typically located at the distal end of at least one subcutaneous implanted electrode line connected to the implantable cardiac monitor. Implantable cardiac stimulators such as pacemakers, defibrillators and cardiac resynchronization devices, generally employ electrodes located at the distal end of electrode lines that are implanted in the heart chambers and connected to the implanted device and may also provide the functionality of an implantable cardiac monitor. Cardiac events are typically detected by analyzing the electrical activity of the heart, e.g. by detecting cardiac intervals, for example, but not limited to the QRS complex. Generally, from the time intervals between detected QRS complexes, the heart rate may be derived. Typically, additional diagnostic information may be derived from the characteristics of the cardiac interval or the QRS complex.
Atrial fibrillation (AF) is generally an abnormal high heart rate originating from the atrium of the heart. Implantable cardiac monitors may typically detect AF and store snapshots of cardiac activity before and during detected AF for further analysis. Stored snapshots and other data of the implantable cardiac monitor may generally be transmitted using short range (inductive) or long range (RF) telemetry to devices external to the body, to remote devices or central servers for further analysis.
Generally, detection of cardiac activity may have interference due to noise. Signals with interference by noise may typically be misinterpreted as cardiac activity, e.g. a noise portion may be misinterpreted as QRS complex, leading to false AF detections. These false AF detections are generally due to the irregular nature of false QRS detections arising from noise at the electrodes. In such cases, the implantable cardiac monitor may generally present snapshots of cardiac events that show frequent examples of atrial fibrillation (AF) snapshots due to noise, when AF is not present.
Typically, during AF detection, the AF detection attempts to terminate within a confirmation period after detection of AF. Generally, if AF detection is not terminated by the end of the confirmation period, AF is declared and an AF snapshot is stored. The AF detection will typically terminate once a programmed number of consecutive intervals packets are found to be stable. Sometimes during a high noise presence, noise is generally misclassified as QRS detections rather than as noise. Typically, these misclassifications may lead to false unstable intervals. These unstable intervals generally don't allow AF detection to terminate and therefore lead to AF confirmation, which, results in AF confirmations that show a large amount of noise detections in the snapshots. Generally, AF detection in known devices ignores intervals with noise and removes such intervals from consideration of AF detection or termination.
AF snapshots that show a high presence of noise and no clear AF detection typically do not offer any clinical advantage to the patient. In addition, generally, these snapshots may cause mistrust of the device classification of AF.
Such false AF snapshots are not desired. Therefore, in view of the above, there is a need for an improved device and method to detect atrial fibrillation.